One aspect relates to a medical implant, for example, an implantable stimulation electrode, having a tight substrate and a porous contact region. One aspect also relates to a lead of a cardiac pacemaker having an implantable stimulation electrode and to a method for manufacturing a medical implant, for example, an implantable stimulation electrode.
Medical implants of different types generally have to meet multiple requirements. They need to be biocompatible and integrate well into surrounding body tissue. Further requirements depend on the nature and/or type of the medical implant. Accordingly, prostheses, for example articular prostheses, need to have high stability. Implantable stimulation electrodes of cardiac pacemakers for implantation into the heart need to show good electrical conductivity and low impedance in order to transmit stimulatory pulses effectively to the heart tissue to be stimulated without over-straining the battery of the cardiac pacemaker and exhausting it prematurely. They also need to have a low input impedance in order to be sensitive to the electrical signals from the heart that are monitored by the cardiac pacemaker and to whose irregularities or absence the cardiac pacemaker responds through electrical stimulatory pulses.
In order to harmonize the various requirements, articular prostheses sometimes include a stable core regions of which are surrounded by a porous material. This is generated, for example according to U.S. Pat. No. 4,612,160 A, in that a section of a prosthesis with a smooth surface is provided with a layer of sinter particles that are sintered to it. The irregular and porous surface structure generated by this means promotes the integration of the prostheses into a bone through bone tissue growing into the pores.
In the case of implantable stimulation electrodes, it is customary to manufacture a substrate that forms the core of the stimulation electrode from a solid piece of metal by milling or lathing with a machine, for example from platinum or a platinum-iridium alloy (PtIr). Subsequently, a porous structure made of a similar or the same biocompatible material is sintered onto the solid and polished substrate. Said manufacturing process necessitates several individual working steps. This applies, for example, to the manufacturing of the substrate and/or form body onto which the porous structure is subsequently sintered and, if applicable, to the generation of transverse drill holes or longitudinal slits and the de-burring after a lathing step.
The corresponding medical implants and/or implantable stimulation electrodes form the extreme distal end of a lead of a cardiac pacemaker that leads from a body pocket, in which the cardiac pacemaker is accommodated, though a caval vein to the heart. The stimulation electrode is anchored in the cardiac wall through barbed hooks.
Following the implantation of the stimulation electrode in the cardiac wall, a fibrous capsule with a thickness of up to 3 mm may form around the stimulation electrode as a defense reaction, which impairs the electrical coupling of the stimulation electrode to the tissue by increasing the output and input impedance. The formation of said capsule is being reduced, if applicable, through the administration of pertinent active substances.
The porous surface structure of the head of the stimulation electrode, which forms a contact region of the stimulation electrode, also reduces the defense reaction and facilitates the ingrowth of cardiac wall tissue into the pores of the stimulation electrode. This enables good electrical contact both for the application of stimulatory pulses into the cardiac wall and for measurement of electrical fields in the cardiac wall.